1. Field of the Invention
This invention relates to devices and circuitry for measuring characteristics of a magnetic recording head which is flying in an air bearing relationship over a rotating magnetic recording disk.
2. Description of Prior Art
In current magnetic recording disk files, a magnetic recording head mounted in an air bearing slider assembly is supported in close proximity to a rotating magnetic recording disk. With present disk files, this spacing is less than 20 microinches and the trend for future files is to even smaller spacings in order to increase areal recording density. With such small spacings and relatively fragile suspension mechanism for the slider, any disturbance of the air bearing which results in contact between the slider and the rotating disk can lead to disaster for both the slider and the disk. This problem is complicated with those disks which contain load-bearing particles, such as Al.sub.2 O.sub.3, since such particles often extend above the disk surface and hence have an increased chance of being contacted by the slider.
In this environment, it would be useful to have the ability to test an assembled disk file to determine the amount of contact between the rotating disks and their associated slider assemblies and to remove any disk which appeared to result in excessive contact with a slider assembly.
Glide height testing on current magnetic disk files measures induced head/slider motions that result from the interaction of the slider and any disk defect or asperity on the disk surface. There are several problems with this approach:
1. Special test sliders are required.
2. The dynamics of each test slider must be calibrated.
3. The response of a slider to a disk defect, particularly a narrow particle such as Al.sub.2 O.sub.3 in the disk, depends not only on the defect height but also upon the stiffness of the particle in the substrate and the stiffness of the air bearing.
4. The transducer used in the test slider is generally not part of the magnetic function in the file. Hence, either special test sliders are required, or the slider is fabricated with extraneous, non-magnetic devices.